Aerial lift platform leveling apparatus and system

ABSTRACT

Apparatus and system for leveling the work platform or basket of an aerial lift. A vertical seeking pendulum is mounted on the boom of the lift independent of the platform. Changes in the relative angle between the pendulum and boom are transposed into control signals by means of an epicyclic gear train. The control signals operate an actuator for pivoting the platform in a direction to maintain a level orientation. Platform movement relative to the boom generates a feedback signal which is carried through the epicyclic gear train to cancel the control signal. In one embodiment the pendulum is damped by means of a pair of balls guided in a circular raceway so as to follow the pendulum independent of the boom position. In another embodiment pendulum movement is damped by means of a viscous liquid constrained within a housing so as to surround the pendulum independent of boom position. The system includes a control circuit incorporating a reversible pump selectively operable in one mode to direct fluid to the leveling actuator and through a two-way valve into an hydraulic actuator for raising and lowering the boom, and in another mode to direct fluid to the leveling actuator for moving the platform to its stowed position. An emergency supply circuit directs return fluid from the boom actuator to the leveling actuator as the boom is lowered should the primary hydraulic power source by inoperable for any reason.

United States Patent [191 Gellatly AERIAL LIFT PLATFORM LEVELING APPARATUS AND SYSTEM [75] Inventor: Robert K. Gellatly, Los Gatos, Calif.

[73] Assignee: General Cable Corporation, San

Carlos, Calif.

22 Filed: Feb. 14, 1974 21 Appl. No.: 442,641

Primary ExaminerReinaldo P. Machado Attorney, Agent, or Firm-Flehr, Hohbach, Test, Albritton & Herbert ABSTRACT Apparatus and system for leveling the work platform or basket of an aerial lift. A vertical seeking pendulum 14 1 Jan. 14, 1975 is mounted on the boom of the lift independent of the platform. Changes in the relative angle between the pendulum and boom are transposed into control signals by means of an epicyclic gear train. The control signals operate an actuator for pivoting the platform in a direction to maintain a level orientation. Platform movement relative to the boom generates a feedback signal which is carried through the epicyclic gear train to cancel the control signal. ln one embodiment the pendulum is damped by means of a pair of balls guided in a circular raceway so as to follow the pendulum independent of the boom position. In another embodiment pendulum movement is clamped by means of a viscous liquid constrained within a housing so as to surround the pendulum independent of boom position. The system includes a control circuit incorporating a reversible pump selectively operable in one mode to.

direct fluid to the leveling actuator and through a twoway valve into an hydraulic actuator for raising and lowering the boom, and in another mode to direct fluid to the leveling actuator for moving the platform to its stowed position. An emergency supply circuit directs return fluid from the boom actuator to the leveling actuator as the boom is lowered should the primary hydraulic power source by inoperable for any reason.

20 Claims, 9 Drawing Figures PATENTEI] JAN 1 4 875 I 3.880.088 SHEET 30F 4 FlG.-7

AERIAL LIFT PLATFORM LEVELING APPARATUS AND SYSTEM BACKGROUND OF THE INVENTION This invention relates in general to aerial lifts and in particular relates to aerial lifts incorporating work platforms or baskets carried on the end of an elevating boom.

In conventional aerial lifts of the type described various means have been provided to insure that the work platform or basket maintains a level orientation as the boom is raised and lowered so that the workman can effectively perform his tasks as he rides within the basket. One example of such a prior art leveling system is that which employs master-slave hydraulic actuators. In such a system a master actuator is mounted at the base of theboom so as to extend and retract as the boom is raised or lowered. Flexible hoses from the master actuator communicate fluid to a slave actuator at the opposite end of the boom to pivot the platform in a direction to maintain a level orientation. The masterslave system, however, has not been found satisfactory for various reasons. Thus, the long flexible hoses required between the actuators are expensive and are subject to damage and failure, and any slight fluid leakage from the system, or air entrainment in the fluid, results in off-center leveling so that constant adjustment and maintenance is required.

Another platform leveling system which has been proposed for aerial lifts is that in which a level sensing device is mounted on the platform and is adapted to operate a platform leveling actuator. Such a system also has disadvantages and limitations. Thus, it is necessary to provide flexible hydraulic hoses leading to and from the leveling system on the platform. Furthermore, a problem known in the art as hunting arises because the platform itself acts as a pendulum so that platform movement causes undesirable vibrations which are fed back into the level sensing device.

Certain of the prior art leveling systems for aerial lifts, such as those which are mounted on vehicles, employ means for pivoting the platform to a stowed position so that the boom can be lowered and stowed for transport between work locations. Heretofore control systems which employ convention platform leveling means of the type described have required separate valves and circuitry on the platform for this function. The result is not only the requirement of providing additional equipment for the stowing function but also for stowing it is necessary for the workman to operate controls which are located on the platform.

OBJECTS AND SUMMARY OF THE INVENTION It is a general object to provide new and improved apparatus and system for maintaining a level orientation for the platform of an aerial lift.

Another object is to provide platform leveling apparatus and system of the type described which employs a vertical seeking pendulum mounted on the boom of an aerial lift so as to generate control signals for operating a platform leveling actuator, with movement of the platform generating feedback signals which concel the control signals.

Another object is to provide platform leveling apparatus and system of the type described in which the control signals are generated by the pendulum through an epicyclic gear train, and in which the feedback sigdependent of boom position.

Another object is to provide platform leveling apparatus and system of the type described which includes provision for controlling movement of the platform to its stowed position by means of the platform leveling circuitry and with stowing control actuation being carried out at a location remote from the platform.

Another object is to provide platform leveling apparatus and system of the type described in which a source of pressurized fluid for operating the leveling system is provided by return fluid from the boom actuator as the boom is lowered should the usual fluid pressure supply become inoperable for any reason.

The present invention is characterized in that a pendulum is pivotally mounted on the boom of an aerial lift to freely seek a constant vertical orientation independent of the platform which is being leveled. An epicyclic gear train generates a control signal responsive to a change in the relative angle between the pendulum and boom, and the control signal operates an actuator for pivoting the platform in a direction to maintain the platform in a level orientation. Movement of the platform relative to the boom is returned as a feedback signal through the epicyclic gear train to cancel the control signal. In one embodiment movement of the pendulum is damped by a pair of balls which freely roll within a circular raceway to bear against the pendulum independent of the position of the boom. In another embodiment the pendulum is damped by a volume of viscous fluid which is constrained within a housing to surround the pendulum independent of the boom position. The control circuit for operating the leveling system includes means to remotely stow the platform by operating the fluid pump in a direction opposite of that employed for raising and lowering the boom. The circuit employs means to supply fluid to the platform leveling system by utilizing return fluid from the boom actuator should the normal fluid supply system become inoperable.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a mobile aerial lift having a work platform or basket and which incorporates a platform leveling system in accordance with the invention;

FIG. 2 is a fragmentary side elevation view to an enlarged scale of the platform of FIG. 1;

FIG. 3 is an end elevation view of the platform shown in FIG. 2;

FIG. 4 is a cross-sectional view to an enlarged scale of the leveling control module used with the platform of FIGS. 1-3;

FIG. 5 is a cross-sectional view taken along the line 55 of FIG. 4;

FIG. 6 is a sectional view of another embodiment of the leveling control module of the invention;

FIG. 7 is a cross-sectional view taken along the line 7-7 of FIG. 6.

FIG. 8 is a schematic diagram of the control circuit for the invention; and

FIG. 9 is a schematic diagram of another embodiment showing a modified holding valve arrangement for the circuit of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings FIG. 1 illustrates generally at 10 a mobile aerial lift of the type employed, for example, by a utility company in servicing power or telephone lines and the like. The aerial lift includes a vehicle 11 which carries a turret 12 rotatable about a vertical axis with the turret in turn carrying a telescoping boom 13 adapted to pivot about a horizontal axis through operation of hydraulic actuator 14. The outer end section 16 of the boom is mounted for telescoping extension and retraction through operation of a suitable actuator carried within the boom lower section. A workmans platform or basket 18 is pivotally mounted to the distal end of boom outer section 16, and the platform is illustrated in FIG. 1 as being disposed in a horizontal level orientation at which a workman within the basket has convenient access to the adjacent power line or other work area. As will subsequently be described platform 18 is adapted to be pivoted rearwardly through an arc to a stowed position generally parallel with the axis of the boom. In the stowed position with boom section 16 retracted the boom is adapted to be lowered with platform carried within a recess 19 formed in the vehicle body to facilitate transport between work sites.

FIGS. 2 and 3 illustrate details of the construction of platform 18 and the platform leveling apparatus. The

illustrated platform is formed of open frame construction with a rectangular bottom floor 21 supported from four upwardly extending corner rails 22, 23, brace rails 24, 25, side rails 27 and peripheral top rails 28,29. A pivot axle 31 is mounted on brackets 32 secured to the upper side of the platform with .the axle extending outwardly from a side of the platform. The end of this axle is rotatably mounted in bushings carried between a pair of brackets 34, 35 which are mounted to and depend downwardly from a collar 37 secured about the distal end of outer boom section 16.

For platform leveling and stowing functions, platform 18 is pivotally moved about the axis defined by axle 31 by means of an extensible hydraulic actuator 38. The head end of this actuator is pivotally mounted to an extension of bracket 34 and the rod end is pivotally mounted to a pin 39 carried by a bracket 41 mounted between brace rails 24, 25. Extension and retraction of actuator under the influence of the control system of FIG. 8 pivots the platform through an angle relative to the longitudinal axis of the boom.

A leveling control module 42 is mounted across brackets 34, 35 beneath the boom distal end to provide an automatic leveling control for the platform as the boom is raised and lowered. Hydraulic supply and return conduits 142, 179 extend along the inside of the boom to direct fluid to and from the control module from the fluid pump and control valve elements of the 4 control circuit which, are contained within the vehicle body. Conduits 168, 169 direct fluid pressure, which serves as a control signal, between the control module and platform actuator- 38. A sprocket 48 is mounted for rotation with the end of axle 31 which is mounted to pivot with the platform. A suitable endless chain 49 driven by the sprocket 48 is trained around a sprocket 51 keyed to a shaft 52 extending outwardly from control module 42. Pivotal movement of the platform relative to the boom thereby pivots sprocket 48 to drive chain 49 and provide a feed-back signal into the control module.

FIGS. 4 and 5 illustrate details of leveling control module 42, with the outer housing thereof removed for clarity. An elongate pendulum 53 is mounted at its upper end 54 for free swinging movement about an output valve shaft 56 which in turn is mounted for pivotal movement within frame sides 57, 58 about a first axis 59. A bushing 61 mounted about the output shaft provides positional spacing of the pendulum arm from frame side 57. An axle 62 carried at the lower end of the pendulum arm extends along a second axis 63 parallel with the first axis 59. First and second idler gears 64, 65 are fixedly mounted on axle 62 by means such as set screws 67, 68 with the axle and idler gears being free to rotate relative to the pendulum arm. An input gear 69 is secured by means such as set screw 71 to a bushing 72 which spaces this gear from frame side 58, and this bushing in turn is mounted for free rotation about output shaft 56. Input gear 69 is in meshing engagement with first idler gear 64. An output gear 73 is mounted about output shaft and secured thereto by means such as set screw 74. Output gear 73 is in meshing engagement with second idler gear 65 but is free to rotate relative to the upper end of the pendulum arm and input gear 69. The input gear is also in meshing en- 'gagement with a feedback signal gear 76. The feedback signal gear is secured by a set screw 77 about the axle 52 which carrys sprocket 51 (FIG. 2). Bushing 78 mounted about axle 52 properly spaces gear 76 between the two frame sides for engagement with input gear 69. The pitch diameters of the feedback gear, input gear, idler gears and output gear are calculated utilizing known epicyclic gear train formulas based upon the desired reduction ratio between the input and output gears.

Output shaft 56 from the epicyclic gear train drives a suitable flow control valve 79 which is adapted to direct pressurized fluid from supply conduit 142 into either delivery conduit 168, 169, depending upon the direction of pendulum movement, to leveling actuator 38, and to direct return fluid from the actuator 38 through return conduit 179. The construction and operation of control valve 79 is broadly conventional and thus will not be described in detail.

Means for damping pendulum movement is provided and comprises a pair of relatively large masses 81, 82, such as steel balls, having a circular or spherical configuration and which are constrained for rolling movement on opposite sides of the lower end of pendulum arm 53 within a circular raceway 83 which is concentric with the axis 59 of pendulum movement. The raceway comprises a curvilinear bottom wall 84 and upwardly extending side walls 86, 87. The raceway provides a range of travel for the balls so that they seek their own level due to gravity and thus are free to roll along the-raceway with the pendulum as the boom is raised and lowered. Because the balls, at any position along the raceway, rest on a slight incline on the raceway (as shown in FIG. 5) any pivotal movement of the pendulum arm other then that due to gravity will be resisted by the weight of either ball because the pendulum does not have sufficient energy to move the ball up the incline. The result is that any vibrational movement of the pendulum arm is quickly damped out by the balls so that any hunting effects are minimized. At the same time, the balls freely seek their own level along the incline and will thus easily move with the pendulum as the latter seeks a vertical position when the boom is raised or lowered. Pendulum damping is therefore not influenced by boom position.

During the phase of operation of control module 42 in which a leveling signal is generated, the gear train operates in an epicyclic mode. Thus, assuming that the boom has moved through a small vertical angle so that platform 18 is carried to an orientation slightly off true vertical, pendulum arm 53 together with the damping balls are urged by gravity to a true vertical orientation. This results in angular swinging movement of the pendulum arm relative to the control module. The pendulum arm swings about axis 59 carrying with it idler gears 64 and 65. At this time feedback signal gear 76 and input gear 69 are stationary relative to the module because no feedback signal has yet been generated. The epicyclic gear train movement thus rotates output gear shaft 73 and 59 through a small angle which in turn cracks open valve 79 to direct pressurized fluid through one of the conduits 168, 169, depending upon the direction of pendulum movement, to either extend or retract platform actuator 38.

As the platform pivots relative to the boom, the platform axle drives sprocket 48, feedback chain 49 and sprocket S1 to turn feedback gear 76. The gear train now operates in a nonepicyclic mode for nulling the control signal. Pendulum arm 53 is assumed to be stationary with respect to the control module. Rotation of feedback gear 76 drives input gear 69 which in turn conjointly drives the two idler gears 64, 65. Idler gear 65 drives output gear 73 and output shaft 56 in an opposite direction to that previously described, for closing the valve. The foregoing operating sequence is incrementally repeated so that the platform is incrementally leveled throughout the range of boom travel.

FIGS. 6 and 7 illustrate details of another embodiment of the invention providing a leveling control module 89 which incorporates an epicyclic bevel gear train. A pendulum arm 90 is mounted at its upper end to the hub 91 of a bevel idler gear 92 and is secured thereto by means such as set screw 93. Idler gear 92 in turn is mounted on a sleeve bearing 94 for free rotational movement about the axis 96 of an output valve shaft 97 which is rotatably mounted at one end within module housing 98. The opposite end of shaft 97 is mounted within a sleeve bearing 99 about which a bevel input gear 101 is mounted for free rotation. The outer hub 102 of the input gear in turn is rotatably mounted within the lower end of module housing 98. A feedback sprocket 103 is secured about the outwardly projecting end of hub 102 by means such as set screw 104. A drive sprocket 106 which is fixedly secured to the pivot axle 107 between the platform and boom drives feedback sprocket 103 through a suitable endless chain 108 to provide a feedback signal. A bevel output gear 109 is mounted for rotation on spider 111 about an axis 112 extending radially of output shaft axis 96. Opposite teeth of output gear 109 are in meshing engagement with idler gear 92 and input gear 101. Spider 111 is secured by suitable means such as a key 113 for rotation with output shaft 97.

The outwardly projecting end of output shaft 97 drives a suitable flow control valve 114 of a construction and operation similar to that described for the embodiment of FIG. 1-5. That is, rotation of output shaft 97 controls valve 114 to direct pressurized fluid from supply conduit 1 16 into either of conduits 117, 118, depending on the direction of pendulum movement, for delivery to the platform actuator for pivoting the platform in a direction to maintain a level orientation, with return fluid being directed back to reservoir through conduit 119.

A volume of viscous liquid 121 is constrained within a chamber 122 formed in housing 98. An example of the liquid is a silicone fluid such as phenylmethylpolysiloxane selected to have a viscosity within the range of 50 to 30,000 centistokes, depending upon the particular conditions encountered such as size and weight of the pendulum and ambient temperature. The chamber is of a circular configuration concentric with pivot axis 96 of the pendulum arm. This chamber constrains the volume of liquid to move with the pendulum so that the pendulum is surrounded by fluid independent of boom position. The liquid serves to resist and dampen pendulum movement to minimize the effects of hunting, and at the same time damping is not affected by boom position As the leveling system of module 89 is operating to restore the platform to a level orientation the bevel gear train operates in an epicyclic mode. That is, as the boom moves through a vertical angle pendulum arm remains in vertical orientation under the influence of gravity, and thus there is relative pivotal movement of the pendulum arm with respect to the module housing. This relative movement of the pendulum in turn drives idler gear 92. Because initially the platform is stationary with respect to the boom, feedback sprocket 103 and input gear 101 are similarly stationary with respect to the module housing. Rotation of idler gear 92 therefore drives output gear 109 which in turn drives spider 111 and output shaft 97. Movement of the output shaft cracks open valve 114 to direct pressurized fluid as a control signal into either conduit 117 or 118, depending upon the direction of boom movement, to operate the platform acutator in a direction to return the platform to its level orientation.

Nulling of the control signal is achieved as the platform pivots relative to the boom driving feedback sprocket 103 and input gear 101. Because the pendulum and idler gear 92 at this time are assumed stationary, output gear 109 is therefore reversely driven to carry the spider and output shaft in a reverse direction to close valve 114 and cancel the control signal. This sequence of operation is incrementally repeated for continued platform leveling as the boom moves throughout its range of travel.

FIG. 8 illustrates a schematic diagram of a control system 123 for the invention. The control system includes a suitable reversible or bi-rotational hydraulic pump 124, preferably of the intermeshing gear type, driven by a selectively reversible motor 126, preferably an electric motor. The pump is provided with first and second ports 127, 128 with the motor being adapted to drive the pump in a first mode drawing fluid under suction through first port 127 and directing it under pressure through second port 128, and in a reverse or second mode drawing fluid under suction through the second port and directing it under pressure through the first port. Supply fluid is directed to the ports from reservoir 129 through filter 131 and branch supply conduits provided with one-way flow valves 132, 133. Suitable pressure relief valves 134, 135 are provided downstream of the pump outlets to discharge fluid to the reservoir when the discharge pressure exceeds preset values. I

In the first mode of pump operation fluid under pressure is supplied through conduit 137 for operating the boom. A pressure compensated flow control valve 138 is provided in conduit 139 to permit free backward flow toward the pump, and to limit forward flow to boom actutor 141 to create a back pressure in supply concuit 142 for driving the platform leveling actuator 143. Flow from valve 138 is directed into a suitable four-way three position directional flow control valve 144. Directional control valve 144 may be a spool valve which is selectively operable from its illustrated neutral position to either elevate or lower positions by operator controlled servo units 146, 147, respectively. To elevate the boom the operator energizes servo unit 147 to shift the spool of the valve to the left, as viewed in FIG. 8, thereby directing pressurized fluid into conduit 148, with return fluid being directed into conduit 149 and return line filter 151 to reservoir 129. Fluid from conduit 148 is freely directed through check valve 152 of holding valve unit 153 and into pressure compensated flow control valve 154. Holding valve unit 153 includes a normally closed pilot operated valve 156 which is adapted to hydraulically lock actuator 141 when control valve 144 is neutral, and to permit return flow through conduit 148 and 161 from the actuator responsive to pressure communicated through pilot conduit 157 when conduit 158 is pressurized to retract actuator 141 for lowering the boom. A pilot conduit 159 is also provided to open holding valve 156 responsive to a predetermined pressure buildup in conduit 161 to serve as a pressure relief function.

Pressure compensated flow control valve 154 permits free flow through its check valve 162 into the head end of the actuator for elevating the boom. This control valve limits return flow from the head end as the actuator is retracted to limit the rate of boom descent.

For lowering the boom the operator energizes servo unit 146 to shift the spool of valve 144 to the right as viewed in FIG. 8, thereby directing pressurized fluid into conduit 158 to the rod end of actuator. A pilot operated pressure relief valve 163 is provided to discharge fluid from conduit 158 to reservoir 129 above a predetermined limit of pressure to insure against damage from overtravel of the boom as it is lowered. Return fluid from the head end of the actuator flows into return line filter 151 and reservoir 129 from pressure compensated flow control valve 154 and 156, which is opened by pressure in pilot conduit 157.

Back pressure generated from pressure compensated flow control valve 138 is directed through check valve 164 into conduit 142 and leveling control valve 79. Pendulum 53 is illuatrated schematically and operates control valve 79 through a gear train arrangement and damping mechanism of the type described for either embodiment of FIGS. 1-5 or FIGS. 6-7. Operation of valve 79 in the manner described directs pressurized fluid from conduit 142 into either of the control signal conduits 168, 169, depending on the direction of pendulum movement, as the leveling control signal. Conduit 169 directs fluid through pilot operated check valve 170 which is opened by pressure through pilot line 171 from supply conduit 142, and into conduit 172 of double holding valve unit 173.. Fluid from conduit 172 flows through check valve 174 and into the head end of actuator 143 which extends to pivot the platform. Return fluid from the rod end of the actuator flows through pilot operated holding valve 176 which is opened by pressure communicated through pilot conduit 177 from conduit 172. The return fluid then continues into conduits 178 and 168, through control valve 79 into return conduit 179 through check valve 181, and into conduits 182 and 183 supplying fluid into port 128 of the pump. Movement of the platform to a level orientation cancels the control signal by closing valve 79 in the manner previously described.

When the pendulum swings in an opposite direction valve 79 directs pressurized fluid from conduit 142 into conduits 168 and 178, through check valve 1840f holding valve 173, and into the rod end of the actuator. As the actuator retracts to pivot the platform in an opposite direction the return fluid from its head end is directed through holding valve 186, which is opened by pressure communicated through pilot conduit 187 from conduit 178. The return fluid continues through conduit 172 and through pilot operated check valve 171 which remains open by the pressure communicated from supply conduit 142. The return fluid continues through valve 79 and check valve 181 into conduit 179 to return to the suction face of pump 124 in the manner described.

Double holding valve 173 hydraulically locks actuator 143 to preclude platform movement when valve 79 is closed. With no pressure in either of the control signal conduits 168, 169 both of the holding valves 176,

186 remain closed to preclude discharge flow from either end of the actuator. Holding valves 176, 186 are adapted to open as a safety precaution when the pressure in either end of the actuator exceeds a predetermined value.

A thermal protection overload relief valve 191 is provided in a branch conduit 192 extending between the control signal conduits 168 and- 169. This valve is normally closed and is opened responsive to the pressure communicated through pilot conduit 193 exceeding a predetermined value. Valve 191 functions to relieve overpressure from thermal expansion of the fluid in the actuator when the system is shut down, and furthermore to relieve overpressure should the platform hit an obstruction as the actuator is being extended.

Means for the emergency lowering of the boom with positive leveling control of the platform is provided. This emergency lowering means includes a solenoid operated check valve 194 in a by-pass line 196 communicating between the control valve 154 from the head end of actuator through a check valve 197 to supply conduit 142. A solenoid 198 controls valve 194 and is powered by a suitable battery power source on the vehicle, for example, operated by a switch located remote from the platform, such as at ground location on the vehicle. When the solenoid is energized for emergency lowering of the boom, as when pump 124 may be inoperative for any reason, check valve 194 is opened so that return fluid is directed from the head end of the actuator into by-pass conduit 196 as the boom lowers. A portion of the return fluid is directed through branch conduit 199 and check valve 201 into conduits 202 and 158 to supply the rod end of the actuator. Another por tion of the return fluid is directed from conduit 196 through check valve 197 and conduit 142 into leveling control valve 79. The leveling control valve thereby can supply fluid to actuator 143 for leveling the platform as the boom is lowered dispite a loss of the normal source of pressure from the pump.

Means for providing remote platform stow capability is provided and includes a branchconduit 203 and check valve 204 connected between conduit 179 and the conduit 172 leading to the head end of actuator 143, as well as a branch conduit 206 and check valve 207 connected between conduit 142 and conduit 178 leading to the rod end. Actuator 143 is mounted so that as it extends the platform is pivoted toward its stowed position relative to the boom. When the operator desires to stow the platform he energizes motor 126 to drive pump 124 in its second mode directing pressurized fluid into conduits 183 and 182, through branch conduit 203 and check valve 204 into conduit 172, through check valve 174 of the holding valve and into the head end of the actuator. Pilot operated check valve 170 is closed due to inadequate pressure in pilot line 171 so that flow is prevented from entering control valve 79 through conduit 169. As the actuator extends return fluid from its rod end flows through holding valve 176, which is opened by pressure from conduit 172, into conduit 178, by-pass conduit 206, check valve 207 and conduit 142. Pilot operated check valve 164 is opened by the pressure in pilot line 208 from conduit 182 to direct the return flow through conduit 137 into the suction port 127 of the pump. When it is desired to return the platform from its stowed position, the pump is operated in its first mode to direct pressurized fluid to leveling control valve 79 which operates in the manner described above to bring the platform to a level orientation.

FIG. 9 is a schematic diagram of another embodiment providing a modified holding valve unit 210 specially adapted to replace the double holding valve unit 173 described for the embodiment of the control circuit of FIG. 8. In holding valve unit 210 control signal conduits 211, 212 are adapted for connection on the upstream sides of, and as a replacement for, the thermal overload valve 191 and conduit 192 described in FIG. 8. When the pendulum swings in one direction the leveling control valve directs fluid under pressure through conduit 212 and check valve 213 into the head end of actuator 214. Pressure from conduit 212 is directed through pilot line 216 to open the opposite pilot operated check valve 217. Return fluid from the rod end of the actuator now flows through the open check valve 217, through conduit 211 and back to the leveling control valve. Reverse pendulum movement operates the leveling control valve to direct pressurized fluid into conduit 211 and through check valve 217 into the rod end of the actuator. Pressure from conduit 211 is directed through pilot line 218 to open check valve 213, thereby permitting return flow from the head end of the actuator to flow through conduit 212 back to the leveling control valve.

Thermal overload relief means is provided and in cludes a normally closed relief valve 219 in a branch conduit 221 connected at one end with control signal conduit 211. The other side of relief valve 219 is connected with a pair of branch conduits 222, 223 each of which is provided with a check valve 224, 226 adapted 5 to permit flow from respective rod and head ends of the actuator only toward valve 219. Should an overpressure condition occur, such as due to thermal expansion in either end of the actuator when the leveling control system is inactive, then this pressure is communicated through either of the check valves 224, 226 for opening valve 219. This overpressure of fluid isthen directed through branch conduit 221 for discharge into conduit 211.

The use and operation of the invention will be demonstrated assuming that the apparatus and control system of the embodiments of FIGS. 1-5 and 8 is adapted for use on the aerial lift of a utility line maintenance vehicle. In the epicyclic gear train within control module 42 it is assumed as an example that feedback signal gear 76 has sixty teeth, input gear 69 has 48 teeth, idler gears 64 and 65 have 72 and 48 teeth, respectively, and output gear 73 has 72 teeth. For epicyclic operation when the pendulum is swinging the foregoing gear arrangement results in a 5/9 reduction ratio for driving output shaft 56 to generate the control signal. For nonepicyclic operation when the pendulum is stationary, the foregoing gear train also provides a 5/9 gear reduction ratio for rotation of feedback signal gear 76 to turn the output shaft in an opposite direction for nulling the control signal.

To raise the boom with automatic platform leveling in effect, the operator energizes motor 126 to drive pump 124 in its first mode, and at the same time servo unit 147 is energized to shift the spool of control valve 144 to the left so that pressurized fluid from the pump and flow control valve 138 is directed through holding valve 153 and flow control valve 154 into the head end of actuator 141. As the actuator extends and raises the boomthe platform is initially carried at a fixed angle with respect to the boom. In the control module pendulum arm 53 freely seeks a vertical orientation so that it undergoes a relative angular movement about axis 59 with respect to the control module housing. With feed back signal gear 76 initially fixed, the gear train operates in an epicyclic mode to rotate output gear 73 and output shaft 56 in a direction to crack open control valve 79. Valve 79 then directs fluid from supply conduit 142 into control signal conduit 169 and through double holding valve 173 to the head end of actuator 143. As the actuator extends to pivot the platform through an angle toward the boom to maintain a level orientation, endless chain 49 drives sprocket 51 and feedback gear 76 which in turn drives the gear train in a non-epicyclic mode to rotate output shaft 56 in an opposite direction for closing valve 79 and shut off flow to the platform actuator. Continued elevating movement of the boom causes incremental operation of leveling control valve 79 in the manner described to maintain a level orientation of the boom.

For lowering the boom the operator energizes servo unit 146 to shift spool valve 144 to the right as viewed in FIG. 8, thereby establishing communication from the pump into conduit 158 and the rod end of actuator 141, with return fluid from the head end being directed through valves 154, 153 and 144 back to the reservoir. As the boom lowers pendulum 53 swings in an opposite direction relative to the module housing, thereby driving the epicyclic gear train to rotate output shaft 56 in an opposite direction from that which occurs during boom elevation. Control valve 79 is cracked open to direct fluid from supply conduit 142 into control signal conduit 168 and through holding valve 173 into the rod end of platform actuator 143. The platform actuator now retracts to pivot the platform through an angle away from the boom toward a level orientation. This causes endless chain 49 to drive sprocket 51, feedback gear 76 and the gear train in a non-epicyclic mode for rotating output shaft 56 in a direction which closes valve 79 to stop movement of the platform. Continued lowering of the boom incrementally operates control valve 79 in this manner to maintain a level orientation of the platform. When the boom is stationary and no control signal is generated by leveling control valve 79, holding valve 173 functions to hydraulically lock actuator 143 in position by precluding fluid discharge from either the head or rod ends.

Whenever necessary in an emergency, such as when the pressure supply from pump 124 fails for any reason, the operator can lower the boom with positive platform leveling control by energizing solenoid 198 to open solenoid controlled check valve 194. This permits fluid from the head end of boom actuator 141 to flow at a controlled rate through pressure compensated flow control valve 154 and through check valve 194, with a portion returning to the rod end of the actuator through branch conduit 199, check valve 201 and conduit 202. Another portion of the return fluid flows through by-pass conduit 196 and check valve 197 into conduit 142 which supplies fluid to leveling control valve 79 for use in maintaining a level orientation of the platform as the boom is lowered.

The control system of the invention makes it feasible for the operator to remotely control stowing of the platform when it is desired to completely lower the boom for transport to another work location. To accomplish this the operator merely reversely actuates motor 126 to drive pump 124 in its second mode delivering pressurized fluid through conduits 183 and 182. This flow is directed through branch conduit 203 and check valve 204 into the head end of actuator 143 through holding valve 173. This causes the actuator to extend to pivot the platform to a position generally parallel with the axis of the boom. To return theplatform to an operating position motor 126 is again reversed to drive pump 124 in its first mode directing pressurized fluid into conduit 137. This provides normal fluid pressure into leveling control valve 166 which, because pendulum 53 has pivoted through a large angle relative to the control modlue housing, generates a control signal through conduit 168 to the rod end of the actuator which retracts to return the platform to its level orientation.

While the foregoing embodiments are at present considered to be preferred it is understood that numerous variations and modifications may be made therein by those skilled in the art and it is intended to cover the appended claims all such variations and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a system for maintaining a substantially horizontally level orientation of a platform which is pivotally connected about a first horizontal axis to the end of the boom of an aerial lift and in which the boom is adapted to be pivotally raised and lowered about a second horizontal axis, including the combination of pendulum means for seeking a constant vertical orientation under the influence of gravity, signal generator means coupled with said pendulum means for generating a control signal responsive to the pendulum means sensing operation of the aerial lift which causes said platform to move through an angle from said level orientation, actuator means for moving said platform about the first horizontal axis in a direction for returning the platform to said level orientation responsive to said control signal, and feedback means for terminating said control signal responsive to return of said platform to said level orientation.

2. A system as in claim 1 which said signal generator means includes a signal output element, means controlling said actuator means responsive to movement of said output element, and gear train means for moving said output element responsive to movement of said pendulum means as the boom and platform are pivoted.

3. A system as in claim 2 in which said output element comprises a rotatable output shaft, and said gear train means includes means forming an epicyclic gear train having an output gear operably connected with said output shaft, an input gear driven responsive to said feedback signal, and gear means driven responsive to said relative movement of said pendulum means for drivingly interconnecting said input and output gear.

4. A system as in claim 3 in which said output gear is mounted on the output shaft for rotation about the axis of the same, said input gear is mounted for relative rotation about the axis of the output shaft, the pendulum means is mounted at one of its ends for pivotal movement about the axis of the output shaft, and said gear means comprising first and second idler gears carried by the other end of said pendulum means and coupled together for rotation about an axis parallel with and spaced from the axis of the output shaft, said first and second idler gears being in meshing engagement with respective input and output gears.

5. A system as in claim 3 in which said output gear is mounted for rotation about an axis extending radially of the axis of said output shaft and said output gear axis is adapted to turn with said output shaft, said input gear is mounted for rotation about the axis of the output shaft and is in meshing engagement with the output gear, and the gear means includes an idler gear which is mounted for rotation with said pendulum means about the axis of the output shaft and is in meshing engagement with the output gear.

6. A system as in claim 3 in which the actuator means comprises an hydraulic actuator, the signal generator means including a source of fluid under pressure, valve means connected with the source of fluid pressure and operable in one mode of direct pressurized fluid to the actuator for pivoting the platform in one direction responsive to rotation of the output shaft in a first direction and in another mode to direct pressurized fluid to the actuator for pivoting the platform in another direction responsive to rotation of the output shaft in a direction opposite of the first direction.

7. A system as in claim 6 in which the feedback means includes drive means for rotating said input gear in a direction to drive the epicyclic gear train for cancelling said control signal responsive to pivoting of said platform in either direction.

8. A system as inclaim 7 in which drive means includes a drive sprocket mounted for rotation with the platform about said first axis, a driven sprocket mounted on the boom in driving connections with said input gear, and endless drive means trained between said sprockets.

9. A system as in claim 1 which includes means for damping the movement of said pendulum relative to the boom, the damping means including a damping mass positioned to resist movement of said pendulum means at an end thereof remote from its pivotal connections with the boom.

10. A system as in claim 9 in which said damping mass comprises a plurality of bodies having a circular outer configuration, and curvilinear raceway means carried by the boom and positioned to constrain the bodies for rolling movement along a path.

11. A system as in claim 10 in which the bodies each comprise spherical balls, and the raceway means is positioned concentric with the pivotal axis of the pendulum means for constraining the balls for movement along the path in contact with opposite sides of the pendulum means.

12. A system as in claim 1 which includes damping means for damping the pivotal movement of the pendulum means relative to the boom, the damping means includes a volume of liquid having a selected viscosity effective to dampen movement of the pendulum means, and housing means for constraining said body of liquid in a region disposed about the end of the pendulum means which is remote from its pivotal connection with the boom whereby movement of the pendulum means is damped independent of the vertical orientation of the boom.

13. A system as in claim 12 in which the housing means forms a circular chamber concentric about the pivotal connection between the pendulum and boom, said chamber being adapted to constrain said body of liquid for movement with the pendulum means as the boom is raised and lowered about its horizontal pivot axis.

14. A system for maintaining a substantially horizontal level orientation of a platform which is pivotally connected about a first horizontal axis to the end of the boom of an aerial lift and in which the boom is adapted to be raised and lowered about a second horizontal axis, including the combination of first hydraulic actuator means for raising and lowering the boom about the second axis, second hydraulic actuator means for pivoting the platform relative to the boom about the first axis, said actuators each having first and second ports, a source of pressurized fluid, fluid circuit means for interconnecting the fluid source with the ports of said actuators and to return fluid therefrom, said circuit means including first valve means selectively operable between first and second positions for directing pressurized fluid to the first and second ports of the first actuator means for operation thereof to respectively raise and lower the boom, platform leveling means for generating control signals responsive to a change in the vertical orientation of said boom, second valve means for directing pressurized fluid to the ports of the second actuator means responsive to the control signals for pivoting the platform in a direction to maintain said level orientation, and an emergency supply circuit for directing return fluid from the first port of the first actuator means to the second valve means during lowering of the boom when the pump means is inoperable.

15. A system as in claim 14 in which the emergency supply circuit includes normally closed valve means being selectively opened to direct a portion of the return fluid from the first port of the first actuator means to the second valve means and to direct another portion of said return fluid to the second port of the first actuator means.

16. A system for maintaining a substantially horizontal level orientation of a platform which is pivotally connected about a first horizontal axis to the end of the boom of an aerial lift and in which the boom is adapted to be raised and lowered about a second horizontal axis, including the combination of first hydraulic actuator means for raising and lowering the boom about the second axis, second hydraulic actuator means for pivoting the platform relative to the boom about the first axis, the first and second actuator means each including pairs of ports adapted to receive pressurized fluid for operation of the respective boom and platform, the second actuator means being adapted to pivot the platform toward a stowed position relative to the boom when pressurized fluid is directed to one of its ports, reversible pump means having first and second outlets, said pump means being selectively operable in a first mode to direct fluid under pressure through its first outlet and in a second mode to direct fluid under pressure through its second outlet, fluid circuit means for interconnecting the pump outlets with the ports of said actuators and to return fluid therefrom, said circuit means including first valve means selectively operable between first and second positions for directing pressurized fluid from the first outlet of the pump to the ports of the first actuator means for operation thereof to raise and lower the boom, platform leveling means including second valve means for directing pressurized fluid to the ports of the second actuator means responsive to a change in the vertical orientation of said boom for pivoting the platform in a direction to maintain said level orientation, and conduit means for directing pres surized fluid from the second outlet of the pump means to said one port of the second actuator means for pivoting said platform to its stowed position when said pump means is operated in its second mode.

17. A system as in claim 16 in which said conduit means includes a first branch conduit with one-way valve means for directing pressurized fluid from the second outlet of the pump means only in a direction to said one port of the second actuator when the pump means is operated in its second mode, and a second branch conduit with one-way valve means for directing return fluid from said second actuator means only in a direction to the first outlet of said pump means when the latter is operated in its second mode.

18. In a system for maintaining a substantially horizontal level orientation of a platform whidh is pivotally connected about a first horizontal axis to the end of the boom of an aerial lift and in which the boom is adapted to be pivotally raised and lowered about a second horizontal axis, including the combination of pendulum means pivotally mounted on the boom and freely seeking a constant vertical orientation under the influence of gravity independent of the position of the boom, signal means for generating a control signal responsive to a change in the relative angle between the pendulum means and said boom, actuator means for moving said platform about the first horizontal axis in a direction for returning the platform to said level orientation responsive to said control signal, and feedback means for terminating said control signal responsive to return of said platform to said level orientation.

19. A system as in claim 18 in which said actuator comprises an extensible hydraulic actuator, and said signal means includes a source of fluid under pressure, valve means for directing pressurized fluid from said source to said hydraulic actuator, and means for operating said valve means responsive to relative movement between said pendulum means and the boom.

20. An aerial lift comprising the combination of a mobile support, a boom pivotally mounted at one end to the support for movement in a vertical plane, a platform pivotally mounted on the other end of the boom for movement about a horizontal axis, a pendulum mounted on the boom and freely seeking a constant vertical orientation under the influence of gravity, signal means for generating a control signal responsive to a change in the relative angle between the pendulum and said boom, actuator means for moving said platform about the horizontal axis in a direction for returning the platform to said level orientation responsive to said control signal, and feedback means for terminating said control signal responsive to return of said platform to said level orientation. 

1. In a system for maintaining a substantially horizontally level orientation of a platform which is pivotally connected about a first horizontal axis to the end of the boom of an aerial lift and in which the boom is adapted to be pivotally raised and lowered about a second horizontal axis, including the combination of pendulum means for seeking a constant vertical orientation under the influence of gravity, signal generator means coupled with said pendulum means for generating a control signal responsive to the pendulum means sensing operation of the aerial lift which causes said platform to move through an angle from said level orientation, actuator means for moving said platform about the first horizontal axis in a direction for returning the platform to said level orientation responsive to said control signal, and feedback means for terminating said control signal responsive to return of said platform to said level orientation.
 2. A system as in claim 1 which said signal generator means includes a signal output element, means controlling said actuator means responsive to movement of said output element, and gear train means for moving said output element responsive to movement of said pendulum means as the boom and platform are pivoted.
 3. A system as in claim 2 in which said output element comprises a rotatable output shaft, and said gear train means includes means forming an epicyclic gear train having an output gear operably connected with said output shaft, an input gear driven responsive to said feedback signal, and gear means driven responsive to said relative movement of said pendulum means for drivingly interconnecting said input and output gear.
 4. A system as in claim 3 in which said output gear is mounted on the output shaft for rotation about the axis of the same, said input gear is mounted for relative rotation about the axis of the output shaft, the pendulum means is mounted at one of its ends for pivotal movement about the axis of the output shaft, and said gear means comprising first and second idler gears carried by the other end of said pendulum means and coupled together for rotation about an axis parallel with and spaced from the axis of the output shaft, said first and second idler gears being in meshing engagement with respective input and output gears.
 5. A system as in claim 3 in which said output gear is mounted for rotation about an axis extending radially of the axis of said output shaft and said output gear axis is adapted to turn with said output shaft, said input gear is mounted for rotation about the axis of the output shaft and is in meshing engagement with the output gear, and the gear means includes an idler gear which is mounted for rotation with said pendulum means about the axis of the output shaft and is in meshing engagement with the output gear.
 6. A system as in claim 3 in which the actuator means comprises an hydraulic actuator, the signal generator means including a source of fluid under pressure, valve means connected with the source of fluid pressure and operable in one mode of direct pressurized fluid to the actuator for pivoting the platform in one direction responsive to rotation of the output shaft in a first direction and in another mode to direct pressurized fluid to the actuator for pivoting the platform in another direction responsive to rotation of the output shaft in a direction opposite of the first direction.
 7. A system as in claim 6 in which the feedback means includes drive means for rotating said input gear in a direction to drive the epicyclic gear train for cancelling said control signal responsive to pivoting of said platform in either direction.
 8. A system as in claim 7 in which drive means includes a drive sprocket mounted for rotation with the platform about said first axis, a driven sprocket mounted on the boom in driving connections with said input gear, and endless drive means trained between said sprockets.
 9. A system as in claim 1 which includes means for damping the movement of said pendulum relative to the boom, the damping means including a damping mass positioned to resist movement of said pendulum means at an end thereof remote from its pivotal connections with the boom.
 10. A system as in claim 9 in which said damping mass comprises a plurality of bodies having a circular outer configuration, and curvilinear raceway means carried by the boom anD positioned to constrain the bodies for rolling movement along a path.
 11. A system as in claim 10 in which the bodies each comprise spherical balls, and the raceway means is positioned concentric with the pivotal axis of the pendulum means for constraining the balls for movement along the path in contact with opposite sides of the pendulum means.
 12. A system as in claim 1 which includes damping means for damping the pivotal movement of the pendulum means relative to the boom, the damping means includes a volume of liquid having a selected viscosity effective to dampen movement of the pendulum means, and housing means for constraining said body of liquid in a region disposed about the end of the pendulum means which is remote from its pivotal connection with the boom whereby movement of the pendulum means is damped independent of the vertical orientation of the boom.
 13. A system as in claim 12 in which the housing means forms a circular chamber concentric about the pivotal connection between the pendulum and boom, said chamber being adapted to constrain said body of liquid for movement with the pendulum means as the boom is raised and lowered about its horizontal pivot axis.
 14. A system for maintaining a substantially horizontal level orientation of a platform which is pivotally connected about a first horizontal axis to the end of the boom of an aerial lift and in which the boom is adapted to be raised and lowered about a second horizontal axis, including the combination of first hydraulic actuator means for raising and lowering the boom about the second axis, second hydraulic actuator means for pivoting the platform relative to the boom about the first axis, said actuators each having first and second ports, a source of pressurized fluid, fluid circuit means for interconnecting the fluid source with the ports of said actuators and to return fluid therefrom, said circuit means including first valve means selectively operable between first and second positions for directing pressurized fluid to the first and second ports of the first actuator means for operation thereof to respectively raise and lower the boom, platform leveling means for generating control signals responsive to a change in the vertical orientation of said boom, second valve means for directing pressurized fluid to the ports of the second actuator means responsive to the control signals for pivoting the platform in a direction to maintain said level orientation, and an emergency supply circuit for directing return fluid from the first port of the first actuator means to the second valve means during lowering of the boom when the pump means is inoperable.
 15. A system as in claim 14 in which the emergency supply circuit includes normally closed valve means being selectively opened to direct a portion of the return fluid from the first port of the first actuator means to the second valve means and to direct another portion of said return fluid to the second port of the first actuator means.
 16. A system for maintaining a substantially horizontal level orientation of a platform which is pivotally connected about a first horizontal axis to the end of the boom of an aerial lift and in which the boom is adapted to be raised and lowered about a second horizontal axis, including the combination of first hydraulic actuator means for raising and lowering the boom about the second axis, second hydraulic actuator means for pivoting the platform relative to the boom about the first axis, the first and second actuator means each including pairs of ports adapted to receive pressurized fluid for operation of the respective boom and platform, the second actuator means being adapted to pivot the platform toward a stowed position relative to the boom when pressurized fluid is directed to one of its ports, reversible pump means having first and second outlets, said pump means being selectively operable in a first mode to direct fluid under pressure through its first outlet and in a second mode to direct flUid under pressure through its second outlet, fluid circuit means for interconnecting the pump outlets with the ports of said actuators and to return fluid therefrom, said circuit means including first valve means selectively operable between first and second positions for directing pressurized fluid from the first outlet of the pump to the ports of the first actuator means for operation thereof to raise and lower the boom, platform leveling means including second valve means for directing pressurized fluid to the ports of the second actuator means responsive to a change in the vertical orientation of said boom for pivoting the platform in a direction to maintain said level orientation, and conduit means for directing pressurized fluid from the second outlet of the pump means to said one port of the second actuator means for pivoting said platform to its stowed position when said pump means is operated in its second mode.
 17. A system as in claim 16 in which said conduit means includes a first branch conduit with one-way valve means for directing pressurized fluid from the second outlet of the pump means only in a direction to said one port of the second actuator when the pump means is operated in its second mode, and a second branch conduit with one-way valve means for directing return fluid from said second actuator means only in a direction to the first outlet of said pump means when the latter is operated in its second mode.
 18. In a system for maintaining a substantially horizontal level orientation of a platform whidh is pivotally connected about a first horizontal axis to the end of the boom of an aerial lift and in which the boom is adapted to be pivotally raised and lowered about a second horizontal axis, including the combination of pendulum means pivotally mounted on the boom and freely seeking a constant vertical orientation under the influence of gravity independent of the position of the boom, signal means for generating a control signal responsive to a change in the relative angle between the pendulum means and said boom, actuator means for moving said platform about the first horizontal axis in a direction for returning the platform to said level orientation responsive to said control signal, and feedback means for terminating said control signal responsive to return of said platform to said level orientation.
 19. A system as in claim 18 in which said actuator comprises an extensible hydraulic actuator, and said signal means includes a source of fluid under pressure, valve means for directing pressurized fluid from said source to said hydraulic actuator, and means for operating said valve means responsive to relative movement between said pendulum means and the boom.
 20. An aerial lift comprising the combination of a mobile support, a boom pivotally mounted at one end to the support for movement in a vertical plane, a platform pivotally mounted on the other end of the boom for movement about a horizontal axis, a pendulum mounted on the boom and freely seeking a constant vertical orientation under the influence of gravity, signal means for generating a control signal responsive to a change in the relative angle between the pendulum and said boom, actuator means for moving said platform about the horizontal axis in a direction for returning the platform to said level orientation responsive to said control signal, and feedback means for terminating said control signal responsive to return of said platform to said level orientation. 